Hmm. Getting warmer. Can you post your .deck somewhere so I can examine it?
Sure. Uploaded on my Google Drive:
https://drive.google.com/file/d/12NOJVtMrx9ZNP9pVGqJMq4SKZpayk5H3/view?usp=shari...
I believe I have identified and patched the issue. Your card naming-scheme hit a nasty edge-case in web-decker's deck parser.
The version of web-decker on beyondloom (http://beyondloom.com/decker/tour.html) already includes the fix, so if you clear your browser's cache you should be able to import a deck there and re-save from it as an HTML export.
Patch definitely worked in the way that now the deck doesn't get ruined when opened via Web Decker.
But exporting still didn't work. Renaming all of the cards also didn't help,
Eventually, I figured that the problem was in the first card's script. I wanted it to play a sound file on a loop during the title screen, and this made HTML file unplayable for some reason. Deleting the script solved the issue. I attached the sound to the "begin" button, so it's a decent compromise. :)
Thanks a lot for the assistance!
Ah, I see. It was possible for a background loop to be queued before Decker had set up an audio context. Fixed.
It's generally not a good idea to have background sound on the first card of a deck, because web browsers will often block audio playback until a user has "interacted" with a page, but Decker certainly shouldn't crash if a script attempts it anyway.